This invention relates, in general, to fabrication of semiconductor products, and more particularly, to fabrication of semiconductor devices on bonded wafers.
Conventionally, intrinsic gettering techniques or methods are used on a single silicon substrate to reduce or prevent process-induced defects and contamination defects that occur during normal processing. These intrinsic gettering techniques or methods are achieved by thermal treatments to the silicon substrate, thus providing a clean defect-free surface for subsequent fabrication of semiconductor devices, as well as locating defect sites or impurity sites in the interior bulk of the semiconductor substrate. Locating these impurity sites or defect sites in the inactive regions of the bulk semiconductor material improves performance levels of yet-to-be-built semiconductor devices on the clean, defect-free surface.
Generally, a bonded wafer is made of two semiconductor substrates that are joined together, thus forming a source or active substrate and a handling substrate.
However, in conventional processing of bonded semiconductor wafers, use of intrinsic gettering methods or techniques is not done, thus degrading yet-to-be-built semiconductor devices. Conventional intrinsic gettering methods are not done because intrinsic gettering methods create impurity sites in the middle of the bulk silicon substrate and since the bonded silicon substrate is polished back, the intrinsic gettering sites are removed by the polishing, thus removing the intrinsic gettering capability from the bonded semiconductor substrate or source wafer. By not providing intrinsic gettering in the source wafer or in an active wafer, semiconductor devices that are going to be built on the source or the active wafer will be negatively affected by process-induced defects and contamination, thereby degrading the performance of the semiconductor devices.
It can be readily seen that conventional intrinsic gettering methods and techniques are severely limited when working with bonded wafers. Also, it is clearly evident that by not providing intrinsic gettering in bonded wafers the performance of semiconductor devices that are built on the active or source wafer will be degraded. Therefore, a method for making an intrinsic gettering region in a source or an active wafer used in a bonded wafer would be highly desirable.